Trunked communications systems have developed extensively over the last two decades. The primary reason for trunking has always been to efficiently use the limited frequency spectrum allocated for such radio communications.
Generally, a trunking system operates on multiple usage of its repeaters by a group of communication units. A system resource controller manages the trunking system and allocates repeaters for communication links. At least one repeater, known as a repeater controller, serves to receive and transmit control commands between the system resource controller and the communication units. Typically, each communication link requires full use of a given repeater's communication resources, such as a pair of radio frequency channels or time division multiplexed time slots. Relative to the repeater, one such resource is inbound (for receiving transmissions), and the other is outbound (for transmitting information).
A procedure for establishing a communication link between two or more communication units typically begins with a request to communicate from a first communication unit. The request is a type of data codeword sent to the system resource controller, and is known in the art as a request Inbound Signaling Word (ISW). It is transmitted on the repeater controller's inbound communication resource. The request ISW identifies the first communication unit and a target group or fleet with whom the first communication unit wishes to communicate (private calls are also known in the art, wherein the request ISW specifically identifies a second communication unit as versus a plurality of target recipients).
The system resource controller then assigns a repeater to support the requested communication. Communication amongst these communication units begins after the system resource controller logs the request and issues a grant to the first communication unit (the grant being a data codeword transmitted as an Outbound Signaling Word (OSW) using the repeater controller's outbound communication resource). Throughout the communication, the system resource controller monitors the repeater assigned to support the communication. When the communication ends, the first communication unit transmits a disconnect word, known in the art as an End of Transmission (EOT), to the system resource controller.
Upon receiving the EOT, the system resource controller releases the repeater, thereby rendering it available to support other communication requests.
Repeater talk-around techniques are also known in the art. This form of communication eliminates communication through a repeater. Repeater talk-around allows use of a repeater's communication resource(s) to link two communication units directly. Such prior art talk-around techniques, however, are restricted to only one pair of communication units for each repeater. Therefore, although the repeater itself is not used, the repeater cannot be used for other communications because its communication resources are being used to support a talk-around communication within the system.
A significant limitation for prior art trunked radio systems is the available number of repeater communication resources. During periods when communication requests exceed the number of available repeater communication resources, users cannot link immediately, but must wait for a resource to become available. A need therefore exists for a way to use the communication resources of a trunked communication system to support an increased number of two-way communications, at least under some operating conditions.